U.S. professor finds longest prime number with 17,425,170 digits

February 08, 2013|Reuters

By Kevin Murphy

KANSAS CITY, Mo., Feb 8 (Reuters) - After running 1,000computers non-stop for 39 days to uncover the world's largestprime number yet, a Missouri college professor said this week heis starting all over to top his own record.

"It's a never-ending job," said Curtis Cooper, a computerscience professor at the University of Central Missouri inWarrensburg. The computers are still running, although findinga higher prime number is estimated to take five to seven moreyears. Thousands of other computers in the United States aremaking the same search.

"This is my first love," Cooper, 60, said in an interviewwith Reuters. "It's pure mathematics. It's kind of an art form."

Cooper said he has received calls and emails from around theworld after Wednesday's announcement that he had identifiedthe prime number - which is a number that can only be divided byitself and 1. For example, 4 is not a prime number because itcan be divided by itself, 1 and 2. Prime numbers include 2, 3,5, 7 and on up to the giant figure Cooper and his computersdiscovered, which has 17,425,170 digits.

The new number is 2 multiplied by itself 57,885,161 times,minus 1. A single campus computer, labeled #22, found the numberon Jan. 25, but it had to be verified by the primenumber locator project known as GIMPS - the Great InternetMersenne Prime Search.

The term "Mersenne" refers to the rarest prime numbers, only48 in all, that have ever been discovered. GIMPS has discoveredthe last 14 of them.

Working with the GIMPS system, Cooper and Central Missourichemistry professor Steven Boone discovered two earlier recordprime numbers, in 2005 and 2006. Their newest prime number isthe largest discovered since 2008, at the University ofCalifornia-Los Angeles. It beat the UCLA number by some 5million digits.

Having the record prime number discovered three times atCentral Missouri, a state college with about 11,000 students, isa source of great pride, said Mike Greife, the school's newsbureau director. "It's kind of mind-boggling," Greife said ofthe search process.

Cooper said his earlier successes finding the highest primenumber motivated him to keep trying. He said he spent at leasttwo hours a day "baby-sitting" the college computers to makesure everything was operating properly. The search software runsin the background while the computers carry out other functions.

Cooper said prime numbers are mostly of interest tomathematicians, but the search has some practical uses. For onething, it shows how computers can be used together on such aproject, he said.

Prime numbers also have been used in Web applications toencrypt messages because they are so rare. Those numbers,though, have a mere 100 to 200 digits, Cooper said.